1. Field of the Invention
The present invention relates to a method of preventing polymer scale deposition on the inner wall and so forth of a polymerization vessel during polymerization of a monomer having an ethylenically double bond.
2. Description of Prior Art
In processes of preparing polymers by polymerizing a monomer in a polymerization vessel, the problem that polymers deposit on the inner wall and other parts which come into contact with the monomer such as stirring blades of the polymerization vessel in the form of scale, is known. The deposition of the polymer scale on the inner wall results in disadvantages that the yield of the polymer and the cooling capacity of the polymerization vessel are lowered; that the polymer scale may peel and mix into manufactured polymer, thereby impairing the quality of the manufactured polymer; and that removal of such polymer scale is laborious and hence time-consuming. Further, since the polymer scale contains unreacted monomer, there is a danger that the workers may be exposed to the unreacted monomer, which may give them some physical disorders.
Heretofore, there are known methods for preventing polymer scale deposition in which the inner wall and so forth are coated with various materials that act as polymer scale preventive agents, for example, particular polar compounds (Japanese Patent Publication (KOKOKU) No. 30343/1970); dyes or pigments (Japanese Patent Publication (KOKOKU) No. 30835/1970); an aromatic amine compound (Japanese Pre-examination Patent Publication (KOKAI) No. 50887/1976); a reaction product of a phenolic compound with an aromatic aldehyde (Japanese Pre-examination Patent Publication (KOKAI) No. 54317/1980)
These methods are effective in preventing polymer scale deposition, in the case where the monomer to be polymerized is vinyl halide such as vinyl chloride or a monomer mixture containing a large amount of vinyl halide and a small amount of other monomers copolymerizable therewith. However, the scale-preventing effect achieved varies depending on polymerization conditions such as the kind of monomers, the ratio of materials charged in a polymerization, the kind of a polymerization catalyst, and the material of the inner wall of a polymerization vessel; it is difficult to prevent the scale deposition effectively and certainly. Specifically, when a polymerization catalyst with a strong oxidative effect such as potassium persulfate, acetylcyclohexylsulfonyl peroxide and di-2-ethoxyethyl peroxydicarbonate is used, the scale preventive agent forming the coating may be oxidized, so that the scale preventing effect is lowered. In the case of polymerization vessels with inner wall made of stainless steel or other steels, polymer scale deposition is liable to occur as compared with vessels lined with glass. Emulsion polymerization is liable to form polymer scale deposition as compared with suspension polymerization.